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Old 07-22-2018, 06:15 AM   #1
Skoolie
 
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Year: 1992
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Letís talk crap about my transmission.

So in my Thomas I have the aftercooled? Dta360 attached to an AT545. Iíve never been a heavy diesel mechanic so I need to know a couple things.
1. Why is the 545 so bad? I understand it doesnít have a ďlockĒ which is constant slip I guess, and itís rated gvwr 30,000 but whats really wrong with that?
2. How can this be made better if possible.
3. Anyone using this transmission to travel?
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Old 07-22-2018, 06:55 AM   #2
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Quote:
Originally Posted by thrifty1 View Post
So in my Thomas I have the aftercooled? Dta360 attached to an AT545. Iíve never been a heavy diesel mechanic so I need to know a couple things.
1. Why is the 545 so bad? I understand it doesnít have a ďlockĒ which is constant slip I guess, and itís rated gvwr 30,000 but whats really wrong with that?
2. How can this be made better if possible.
3. Anyone using this transmission to travel?
Slip=Heat. Efficiency and service life are both affected.
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Old 07-22-2018, 07:55 AM   #3
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Are there any "tighter" torque converters available for it?

My old Dodge had a Cummins 5.9 with the old 3 speed 727. Talk about slip... the engine would reach governed speed (2800rpms) on a heavy pull right away. For this truck there are plenty of much better torque converters with a lower stall speed. This made a huge difference. Engine and tranny outlasted the truck. Wish I still had it.
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Old 07-22-2018, 08:19 AM   #4
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the converter in my DTA360 was pretty decent for an AT545, i had decent engine braking, however i still wasted that transmission.. I consistently drive both my busses on long road trips over mild mountains (3000 feet or so).. in 2 years time I ruined 2 AT545s on 2 different busses.. I drive alot of miles.. 30,000 plus in those 2 years combined on both busses.. maybe closer to 40k by now..



both are short busses.. while i never had issues descending.. I cant help but think my constant driving those busses on the highway and over hills contributed to the failures..


others here have driven that many miles plus on their 545s without a single issue..



the first bus i upgraded to a 6 speed auto OVerdrive allison a year ago..


the second bus im in the process of swapping out to an MT-643 as we speak (bus is in pieces now)..



in a full size heavy bus i could definitely see there being issues descending hills .. at least big ones with a 545.. my DTA360 bus is GVWR 27500. and i simply took it slow on the downhills.. usually slow enough I could run in 3rd gear which had decent engine braking.. get over about 48 though (in that bus) and it would upshift to 4th regardless of my shifter position!!



-Christopher
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Old 07-22-2018, 08:24 AM   #5
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So do you think it would be worth looking into swapping the tranny if I plan on doing N.C. mountain driving eventually? How hard is it to swap/find an mt643 in your experience?
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Old 07-22-2018, 08:35 AM   #6
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im in the process of my DTA360 swap.. theres another thread around here someplkace where I posted what is needed.. theres a couple 643 swap threads up right now..



navistar recently expunged the MT643 from their parts database and dumped all inventory of their ReMan 643s.. LKQ in marshfield Mo. is one place that got a bunch of them.. all reman for navistar DT mechanical engines. and cost about 650 a piece.



the swap.. the 643 is HEAVY.. bur basically you need a different flexplate, cooler line mods, flywheel mounting bolts, shorten the driveshaft, muscles, and a good trans jack.. as far as trans swaps go its straightforward.. but like any major component swap.. you need to be mechanically inclined and have the right tools.. or hire a shop to do the work for you.



thus far into my 643 swap ive found the things ive used are.. engine hoist, pickup truck, air-impact, jacks, 2000 lb ratchet straps, and normal hand tools.. this far i havent used any tool that isnt readily rentable at a place like nationsrent.. I own my own tools simply because i tend to update and upgrade whatever project i get my hands on. driveshaft work is easy.. measure, mark, and take it to a drive-line shop (most every decent size town has one or two).. cooler lines I make new ones with braided steel line and AN fittings.. shift linkage,dipstick tube, reverse lights, speed sensor, neutral safety, modulator.. all the same from 545 to 643 so thats just bolt from old to new.. some parts I bolt from one to the other while both trans are on the ground.
-Christopher
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Old 07-22-2018, 08:43 AM   #7
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cool thread - easy topic



my first bad experience with a 545.

one of my first camping trips out when i first got my bus. i'm in Colorado, so i head up to the mountains. climbing I-70 in 5 lane traffic heading out of Denver. and thats all good! its the trip home that gets you. Coming down i-70 was the problem.
the 545 doesn't engine brake much. you don't realize how much you depend on engine braking, until you don't have it. i tried to roll with traffic (65-70mph) across 5 lanes and i was soon out of control. the transmission screams like you are turning it into shrapnel, free wheels. you stand on the brakes until they smoke and run out of air. it was basically a **** your pants and glad you didnt make the news kind of drive.

thats my AT545.

over heating going up passes. the truck runs uphill and starts slowing down. your rpms stay the same. i was doing 65mph @ 2500rpm's, at the top of a pass you may be doing 1/2 mph at 2500rpms. over heating.

thats my AT545

i had an AT545 and replaced it with another (locking version).
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Old 07-22-2018, 08:49 AM   #8
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Hahaha. Good visuals there. So where did you find a locking version? My bus is a 92 Thomas navistar, were there any with stock trannyís like this? If so how could you tell? Lastly, has the locking version made a huge difference?
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Old 07-22-2018, 08:58 AM   #9
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Learn to enjoy driving slow.

im a better truck driver for surviving my AT545.

the locking version has been trouble free but Chris's wap is the one to do. i have the AT1545 - military version of the 545. but it was never mated to a cummins so the swap needed a custom flexplate. the MT643 is a tried and true swap.
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Old 07-22-2018, 10:11 AM   #10
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Quote:
Originally Posted by turf View Post
cool thread - easy topic



my first bad experience with a 545.
*snip
one of my first camping trips out when i first got my bus. i'm in Colorado, so i head up to the mountains. climbing I-70 in 5 lane traffic heading out of Denver. and that's all good! its the trip home that gets you. Coming down i-70 was the problem.
the 545 doesn't engine brake much. you don't realize how much you depend on engine braking, until you don't have it. i tried to roll with traffic (65-70mph) across 5 lanes and i was soon out of control. the transmission screams like you are turning it into shrapnel, free wheels. you stand on the brakes until they smoke and run out of air. it was basically a **** your pants and glad you didnt make the news kind of drive.
overheard in the bus that day...., "honey, bring me my brown pants!"
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